Determining the Frequency of a String’s Appearance - PHP

Thesubstr_count()function returns the number of times one string occurs within another. Its prototype follows:

int substr_count(string str, string substring)

The following example determines the number of times an IT consultant uses various buzzwords in his presentation:

<?php
    $buzzwords = array("mindshare", "synergy", "space");

    $talk = <<< talk
    I'm certain that we could dominate mindshare in this space with
    our new product, establishing a true synergy between the marketing
    and product development teams. We'll own this space in three months.
talk;

    foreach($buzzwords as $bw) {
        echo "The word $bw appears ".substr_count($talk,$bw)." time(s).<br />";
    }
?>

This returns the following:

--------------------------------------------
The word mindshare appears 1 time(s).
The word synergy appears 1 time(s).
The word space appears 2 time(s).
--------------------------------------------

Replacing a Portion of a String with Another String

Thesubstr_replace()function replaces a portion of a string with a replacement string, beginning the substitution at a specified starting position and ending at a predefined replacement length. Its prototype follows:

string substr_replace(string str, string replacement, int start [, int length])

Alternatively, the substitution will stop on the complete placement ofreplacementinstr. There are several behaviors you should keep in mind regarding the values ofstartandlength:

1. Ifstartis positive,replacementwill begin at characterstart. 
    
2. Ifstartis negative,replacementwill begin atstrlength -start. 
    
3. Iflengthis provided and is positive,replacementwill belengthcharacters long. 
    
4. Iflengthis provided and is negative,replacementwill end atstrlength -lengthcharacters.

Suppose you built an e-commerce site and within the user profile interface you want to show just the last four digits of the provided credit card number. This function is ideal for such a task:

<?php
    $ccnumber = "1234567899991111";
    echo substr_replace($ccnumber,"************",0,12);
?>

This returns the following:

--------------------------------------------
************1111
--------------------------------------------

Please check back next week for the conclusion to this article.